Patent GB-640194-A (GB)
Title: Improvements relating to brake control equipment for braking apparatus for railway vehicles and the like
IPC: B60T8/32
Filed: 1947-12-23
Abstract: 640,194. Fluid-pressure brakes. WESTING. HOUSE BRAKE & SIGNAL CO., Ltd. Dec. 23, 1947, No. 33908. Convention date, Nov. 30, 1939. [Class 103 (i)] A fluid-pressure brake control system for railway vehicles comprises a combination of the following features: (a) the degree of application of the brakes, for a given control pipe pressure is automatically reduced as the speed of the vehicle is reduced; (b) the brakes are auto. matically released when a vehicle wheel or pair of wheels begins to slip; and (c) sanding apparatus is operated to prevent wheel slip. The invention is characterized principally in that the degree of application of the brakes is arranged to be controlled jointly by the value of an electrical quantity and by the rate of change of this value. The system, as shown in Fig. 1, in addition to the usual driver's valve 21, reservoir 19, brake air supply pipe 17, brake air control pipe 18, and brake cylinders 16, as shown, for the front and rear wheel trucks of a single vehicle, includes also a speed-controlled valve mechanism 24 and slip-controlled valve mechanisms 25, one for each wheel truck, interposed between the pipes 17 and 18 and the brake cylinders 16. The manner in which the brake cylinder pressure is automatically reduced with speed is as follows. Assuming that the brakes are released and the cylinders 16 at atmospheric pressure, application is begun by adjusting valve 21 to provide a certain pressure in the control pipe 18 which is transmitted to the valve mechanism 24 by pipe 91. The valve mechanism 24 has a part 52 (similar to the valve device 11 shown in Specification 519,450) containing a number of diaphragms of different area, the movement of which operates a relay valve in part 51 by which reservoir air supplied through pipes 17, 66, 67 is passed on with its pressure reduced in a variable ratio by pipe 64 to the valve mechanisms 25 leading to the brake cylinders 16. This ratio is varied by the operation of one or more of three magnet valves 54, 55, 56, which control the transmission of the control pipe pressure in pipe 91 to chambers formed between the diaphragms in the part 52. The valve mechanisms 25, which are described later, may be assumed to take no part, except to pass on the pressure in pipe 64 to the brake cylinders, in the automatic variation of brake cylinderpressure with speed which takes place as follows. A generator 35 on the axle of a wheel 13 produces a voltage that varies in accordance with the speed of rotation thereof, and transmits current by lines 74, 78, 81 to the low, medium and high magnet valves 56, 55 and 54 respectively. The relays 36, 37 and 38 are arranged to operate to close the switches a and b at currents from the generator 35 corresponding to speeds of approximately 20 m.p.h., 40 m.p.h., and 65 m.p.h., respectively. Thus, when the train is moving at very high speed all the relays 36, 37 and 38 are actuated and the operation of the magnet valves 54, 55 and 56 is such that a pressure substantially equal to the control pipe pressure is passed on by relay valve part 51 to the brake cylinders 16. As the speed of the train is reduced relays 38, 37 and 36 drop successively out of action, thus varying the operative magnet valves 54, 55 and 56 so as to produce through the diaphragm part 52 and relay valve part 51 of valve mechanism 24 a corresponding reduction in the brake pressure transmitted by pipe 64 to the brake cylinders 16. When the train is at a standstill the switch a associated with relay 36 is closed and the low magnet valve 56 only is energized, which provides that a pressure of approximately onethird of the control pipe pressure is passed to the brake cylinders 16. The relay switches bare provided only to switch in or out resistances 41 in the circuits to the lower speed responsive relays 36 and 37 to protect their windings from the currents produced by the generator 35 at high speeds. The current to operate the magnet valves 54, 55, 56 is supplied by a battery 71 through a switch 73. The operation of the wheel slip responsive part of the system is as follows. The generators 35 also energize circuits leading to further relays 43. These circuits include condensers 42 so that the current passed is proportional to the rate of change of voltage, i.e. to the acceleration or deceleration of the wheels 13. If this change, which may be caused by wheel slip, is sufficient, relays 43 are energized. This causes the closing of switches in the circuits of further relays 45 and 46 which thereafter maintain their own energization, independently of relays 43, by current supplied from battery 71 through a switch 96 and lines 95, 98, 99 and 101. Current through the relay 45 returns by line 102, pressure switch 33 which is normally closed, magnet valve 32 controlling the operation of a sanding system to be described later in more detail, and line 104. Operation of the valve unit 32 allows air to flow from a reservoir 31 to carry out the sanding operation. The reduction of pressure in reservoir 31 after a given interval of time effects the opening of pressure switch 33 so that the sanding is discontinued. Current through the relay 46 returns by line 106, pressure switch 27, slip control valve mechanism 25 and lines 108 and 104. When current through this circuit energizes the magnet valve 65 of unit 25 a relay valve part 61 is operated which rapidly vents air supplied to the brake cylinders through pipes 66, 68 and 59, the pressure in the cylinders having, until then, been varied by the pressure supplied to the relay unit 61 through pipe 64 from the speedcontrolled valve mechanism 24. After venting of air from the brake cylinders 16 has taken place so that the pressure therein has been reduced to, say, 10 lbs. per square inch, the pressure switch 27 opens and breaks the circuit. The change of wheel speed has thus resulted in the operation of a sanding device as well as a rapid reduction of the brake cylinder pressure, which operation will be repeated each time the relays 43 become operative. This operation will only take place if a pressure switch 26 has been closed by control pipe pressure in pipe 91. There are similar control circuits for each of the wheel trucks 11 and 12 of a vehicle. The sanding apparatus for each wheel truck includes units 29f and 29r, one pair of wheels only is operative at a time according to the direction of movement of the vehicle. The units shown in Fig. 2 are actuated by air from reservoir 31, which is charged from the main reservoir 19 by pipes 17, 66 and 69, through the magnet valve 32 and valves 29a and 29b. Valves 29a and 29b are alternately opened or closed by a change-over switch in a controlling circuit which must be operated personally by the driver according to the direction in which the train is to travel. Modifications also described and illustrated include a variation of the circuits for the relays 36, 37 and 38 to ensure that they operate at the same speeds whether the train is accelerating or decelerating, and two alternative methods of successively energizing the magnet valves 54, 55 and 56 of the valve mechanism 24. One method uses a pivoted arm having a contact that is moved over four sections of an arcuate terminal plate by a spring-controlled solenoid. The other method uses two pivoted arm switches arranged to make contact after being moved through different angles by the rotation of two armatures between pairs of polepieces. Reference is made to Specification 399,159, which describes a brake valve device similar to that shown at 21.